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Infectious salmon anemia virus

I. General Information

1. NCBI Taxonomy ID:

2. Disease:

Infectious Salmon Anemia

3. Introduction

Infectious salmon anemia or anaemia (ISA) is a viral disease of Atlantic Salmon (Salmo salar) that affects fish farms in Canada, Norway, Scotland and Chile, causing severe losses to infected farms. The disease is listed as a non-exotic disease of the EU and is therefore watched closely by the European Community Reference Laboratory for Fish Diseases. The aetiological agent of ISA is the infectious salmon anemia virus (ISAV). ISAV, a RNA virus, is the only species in the genus "Isavirus" which is in the family Orthomyxoviridae. As the name implies, it causes severe anemia of infected fish. Unlike mammals, the red blood cells of fish have DNA, and can become infected with viruses. The fish develop pale gills, and may swim close to the water surface, gulping for air. However, the disease can also develop without the fish showing any external signs of illness, the fish maintain a normal appetite, and then they suddenly die. The disease can progress slowly throughout an infected farm and, in the worst cases, death rates may approach 100%. Post-mortem examination of the fish has shown a wide range of causes of death. The liver and spleen may be swollen, congested or partially already dead. The circulatory system may stop working, and the blood may be contaminated with dead blood cells. Red blood cells still present often burst easily and the numbers of immature and damaged blood cells are increased (Wiki: Infectious Salmon anemia virus).

4. Microbial Pathogenesis

The major port of ISAV entry is most likely the gill, but oral entry cannot be excluded. Endothelial cells are one of the main target cells for ISAV, but the presence of virus in other cell types including polymorphonuclear leukocytes has been reported. The pathological changes observed in natural outbreaks of ISA may vary between the individual fish and between outbreaks (Rimstad and Mjaaland, 2002).

5. Host Ranges and Animal Models

Apart from Atlantic salmon, both sea-run Brown trout (Salmo trutta) and Rainbow trout (Onchorhyncus mykiss) can be infected, but do not become sick, so it is thought possible that these species may act as important carriers and reservoirs of the virus (Wiki: Infectious Salmon anemia virus).

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